9.12: Student Responses

1. Type 19 53 48.36 N 155 34 58.11 W in the search bar on Google Earth, and zoom out to an eye altitude of ~615 miles. The magma that resulted in the formation of these islands was generated by what process?

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

2. Type 50 16 27.25 N 29 22 05.11 W in the search bar on Google Earth, and zoom out to an eye altitude of ~2663 miles. The magma generated at this location is due to:

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

3. Type 36 11 46.85 S 71 09 48.03 W in the search bar on Google Earth, and zoom out to an eye altitude of ~ 2865 miles. The magma responsible for this volcano was generated by what process?

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

4. Type “San Andreas Fault” in the search bar on Google Earth; no magma is generated here, because this plate boundary is _____________________.

a. a divergent plate boundary, with decompression melting occurs

b. a convergent plate boundary, where water lowers the melting temperature of rock

c. a transform plate boundary, where no magma is produced

5. A(n) ________________________ at the Mid-Ocean Ridge, where oceanic plates are diverging and magma is generated by partial melting of the mantle.

a. ultramafic magma is produced

b. mafic magma is produced

c. intermediate magma is produced

d. felsic magma is produced

6. Type 19 28 19.70 N 155 35 31.94 W in the search bar on Google Earth, and zoom out to an eye altitude of ~119 miles. This volcano is composed of:

8. Type 36 40 41.62 N 108 50 17.22 W in the search bar in Google Earth. The dark-colored rock that forms a straight line on the surface is most likely:

a. a pluton of ultramafic rock.

b. a dike of ultramafic rock.

c. a sill of mafic rock.

d. a dike of mafic rock.

9. Intermediate lavas can flow _____ than mafic lavas, due to the _______viscosity.

a. slower, higher

b. slower, lower

c. faster, higher

d. faster, lower

10. Let’s relate food items to magmas of different viscosity; if we compare how honey and water flow when poured from a container:

a. Then, the honey represents felsic magma while the water represents mafic magma

b. Then, the honey represents mafic magma while the water represents felsic magma.

11. Imagine putting the honey in the refrigerator overnight; will its viscosity be affected?

a. Yes. The viscosity will increase.

b. Yes. The viscosity will decrease.

c. No. There will be no change as the composition stays the same.

12. Keep the honey in mind while you answer this question: when it first erupted, basalt lava typically erupts at 1200°C; after flowing away from the vent, the temperature falls, therefore the viscosity of the basaltic lava will:

a. increase

b. decrease

c. stay the same

13. Type 43 25 04.18N 113 31 37.38 W in the search bar of Google Earth. Zoom out to an eye elevation of ~90 miles. Based on the size of the area which is dark-colored and sparsely vegetated, this region is:

a. a basaltic dike

b. a shield volcano

c. a lava dome

d. a flood basalt

14. Click on the nearby photo icon (SW of your latitude/longitude coordinate in Question 13) to view a picture of the area as seen from the ground. This is a picture of:

a. a basalt flow

b. a felsic dome

c. a plutonic rock

d. an ultramafic rock

15. How many miles in length is this dark-colored feature? (measure the greatest length)

a. ~8 miles

b. ~20 miles

c. ~40 miles

d. ~50 miles

16. Type 46 12 07.84N 121 31 02.85W in the search bar of Google Earth. This volcano (Mt. Adams) has a lot of snow cover and small glaciers on it, but you can still see the volcanic rock, especially on the eastern flank (side) of the volcano. Zoom in to an eye altitude of ~9000ft to closely examine the rocks on this eastern side of the volcano; do you see any evidence of layering? This volcano is:

a. a shield volcano

b. a lava dome

c. a composite volcano

d. a large volcanic dike

17. How tall is Mt. Adams, and what is the length of its base (in the widest, N-S dimension)? You will need to zoom out to an eye altitude of ~17 miles to measure the base.

19. Type in 58 15 58.56 N 155 09 35.98 W in the search bar of Google Earth. Examine the shape of this feature by zooming in to an eye altitude of ~3330 ft; use the eye icon in the upper right corner to rotate the view. Now zoom out to an eye altitude of ~7306 ft to see the entire structure and the surrounding area. Based on the size and appearance of this volcanic feature, this is a:

a. dike

b. shield volcano

c. lava dome

d. flood basalt

20. Type Mount St. Helens, WA in the search bar in Google Earth and examine the crater at an eye altitude of ~26,000 ft. Based on the appearance of the crater:

a. a lahar removed the north side of the volcano

b. a pyroclastic eruption removed the north side of the volcano

c. a lava dome grew so large that it is higher than the north side of the crater

d. a glacier has eroded the north side of the crater

21. Type Mount Rainier, WA in the search bar in Google Earth. The Carbon River flows from the north part of Mount Rainier (fed by meltwater from the Carbon Glacier on the flank of the volcano). At an eye altitude of ~20,000ft, follow the course of the Carbon River, past the town of Carbonado and stop at the town of Orting. Based on the locations of these two towns, which do you think is in danger from a lahar?

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